"Clip Cube" Image Texture extrapolation with default colour?
Assuming I'm getting you correctly, it's not &quot;clip cube&quot;-- it's just, &quot;clip&quot;.  What this does is return 0,0,0,0 RGBA for any vectors that are out of bounds: any vectors with any components that are outside the 0,1 range.
If you want to use a specific color for anything outside of this range, almost like clip border mode does with 0 RGBA, one way to do it is to just check whether the vector is out of bounds:

That's just how I figured to do it with the fewest nodes (no separation nodes): we compare the length of our original vector to the length of our vector clamped to the 0,1 range, and if the original vector is longer, we're out of bounds.  In this case, that means mixing with hot pink.
I said &quot;almost like clip border mode,&quot; because there's one thing clip border mode is doing (or at least should be doing, there used to be an Eevee bug related to this) is texture filtering properly between lookup color and clip color, and doing it this way will not do any kind of texture filtering at the border: you will have a hard-edged border, no matter how little screen space the texels occupy.
Also, because &quot;clip&quot; border mode doesn't actually care about the Z component, only the XY component.  Sending a Z = 1.2 won't clip an image texture lookup, but it will clip the nodes I show above.  If this is important, it's easily fixable-- just scale vector.Z by 0 with a mapping node.